Luffing-crane.



A. H. MITCHELL.

LUFPING CRANE.

APPLICATION FILED JUNE 24, 1912.

1,069,801 Patented Aug. 12, 1913.

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ALFRED HILLYARD MITCHELL, OF PLUMSTEAD, ENGLAND.

LUFFING-CRANE.

Application filed .Tune 24, 1912.

To all whom t may concern:

Be it known that I, ALFRED HILLYARD Mi'rcimLL, a subject of the King ofGreat Britain, residing at 25 Trottesley road, Plumstead, Kent, England,have invented new and useful Improvements in Lufling- Cranes, of whichthe following is a specification.

My invention relates to improvements in cranes of the kind in whichmeans are provided for maintaining the load at one level during luifing.

In cranes of this type as heretofore constructed the maintenance of thelevel of the load has been insured in various ways, as for instance bypaying out or taking in the lifting rope, such an arrangement beingshown, for example, in my prior British Patent No. 8G07 of 1902 or bycausing the jib head to move horizontally by mechanism on the principleof the well-known Scott- Russell straight line motion but in all casesthe weight of the j ib has to be lifted, whereby a considerable waste ofpower is occasioned, and in t-he latter case the length of the cranepost is equal to that of the jib so that the former is unnecessarilylong. Now, according to this invention I construct a crane in such amanner that, as the jib moves in lufiing, its center of gravity moves ina horizontal line whereby the force of gravity on the jib has not to becounteracted in lulling and no balance weight has to be displaced.

In carrying out the invention I make use of a jib the center of gravityof which coincides approximately with its center of length and which issuspended by a link about one-quarter of the length of the jib andconnected to the latter at a point a quarter of the length of the jibfrom the lower end thereof, which end moves vertically up and down thecrane post in the known manner. The lifting rope is passed beneath apulley at the bottom of the post, and over a pulley at the bottom of thejib, and thence over the usual pulley at the jib head. lVith thisconstruction it will be seen that the center of the jib is always at onelevel whatever the position of the jib, and the distance measured fromthe ground to the jib head, added to the length of the jib and thedistance of the jib end from the bottom of the vertical post will remainconstant, notwithstanding the adjustment of the jib during the lutfmgoperation and it Specification of Letters Patent.

Patented Aug. 12,1913.

serial No. 705,540.

will consequently be obvious that if the rope be fixed on the cranebarrel the free end will always have a horizontal travel. Moreover, thejib being so constructed that its center of gravity is at the center ofits length, as it moves in the process of lu'liing, the center ofgravity moves in a horizontal line, thus reducing the power required toluif the jib to a minimum and dispensing with the separate balanceweight.

To enable my invention to be fully understood, I will describe it byreference to the accompanying drawing, in which Figure l is a sectionalside elevation of a lufling crane constructed according to theinvention. Figs. 2 and 3 are respectively a section on the line 2 2,Fig. l, and a plan of a detail drawn to a larger scale. i

a is the jib of the crane which is of the so-called cantaliver type, thesaid jib being suspended at the point by means of a radius rod or linkframe c to the point CZ at the head of the vertical post c of the crane.As above stated the position of the point I) is a quarter, orpractically a quai'- ter of the length of the jib from the lower endthereof, and the radius rod or frame is of a length equal to the saiddistance of the said point from the jib end. A pulley j is mounted atthe head of the jib c and a similar pulley g at the lower end thereof,the lifting rope 7L passing over the said pulleys f and g and thence tothe bottom of the post e where it passes around the pulley tackle of thehydraulic ram c' by means of which the said rope can be drawn in or paidout for the purpose of lifting or lowering the load in the well-knownmanner.

In the construction illustrated, the lower end of the jib a is made ofconsiderable width as shown in Fig. 2 and is provided with rollers j, jwhich run in the channel guides lc, 7c, provided at the lower part ofthe crane post e, the said guides being so constructed that the jibbottom cannot leave the post during the action of sluing. The lufling ofthe crane jib is eHected by means of the hydraulic ram Z and tackle Z1',the latter being connected to the lower end of the jib as shown. Asabove stated the length of the radius rod or link frame c is equal tothe distance between the point and the jib bottom, and the center ofgravit-y of the jib c is at or about the center of its length.

The crane operates as follows z-Assuming that the lower end of the jib abe moved Cit downward along the runway k on the crane post c, then thesaid jib will assume a new position, such, for eXample, as that shown inbroken lines in Fig. l. The lengthof rope, however, from the windingtackle at the bottom of the crane post e over the pulley g along the jiba over the pulley f to the load will remain the same, this being truefor every position of the jib between the maximum and minimum radiusfrom which it will be obvious that any load suspended from the liftingrope 7L will travel in a truly horizontal line when the jib is luffed sothat no work is required to be done on it, neit-her does it do any workor have any effect on the balance of the jib. It will also be obviousthat when the jib is luifed so that the bottom drops vertically to apredetermined extent, the head of the jib will rise to an equal extentin the vertical direction, whereby it results that the center of the jibneither rises nor falls so that it travels in a horizontal line, and ifthe center of gravity of the jib be made to coincide with the cen ter oflength as above stated, the jib is balanced in all positions whetherthere be a load on the lifting rope or not.

In the preceding description I have stated the relative dimensions ofthe jib and its supporting link or links and it will be understood thatthese vdimensions may be somewhat departed from in practice owing to thedifference in the conditions brought about by the wrapping andunwrapping of the rope around the pulleys f and g. It will also be'obvious that any desired area in the travel of the load may be obtainedby suitably modifying the proportions, Apositions and inclinations ofthe various members of the crane gear. It will also be clear that anymeans other than those shown and described may be made use of forcontrolling the lifting and luiiing ropes.

Claims.

1. In a crane of the class described, the combination with a crane post,of a jib, the inner end of which has a sliding connection with saidpost, a radius rod pivotally connected at one end to said post and atits other end to said jib at a point situated about a quarter the lengthof said jib from the inner end thereof, and said radius rod being aboutthe same length as one quarter the length of the jib, and means forvertically moving the inner end of said jib.

2. In a crane of the class described, the

combination with a crane post, of a jib, the

inner end of which has a sliding connection with said post, a radius rodpivotally connectedvat one end to said post and at its other end to saidjib at a point situated about a quarter the length of said jib from theinner end thereof, a pulley provided on the lower end of said jib and afurther pulley provided on the outer end of said jib, a lifting ropepassing over said pulleys, and means for vertically moving the inner endof said jib to increase or decrease the length of the rope between itand a fixed point,

3. In a crane, the combination with a crane post, of a jib, a radius rodor link pivotally connected at one end to said post and at the other endto said jib, means for moving the lower end of the jib in a verticalpath, said jib and radius rod being so proportioned and connected thatthe downward vertical movement of the lower end of the jib is equal tothe vertical rise of the top thereof, whereby the center of gravity ofthe j ib will travel in a horizontal path.

4E. In a crane, the combination with a crane post, of a jib, a radiusrod pivotally connected at one end to said post and at the other end tosaid jib, pulleys provided at the outer and inner end of said jib, arope passing over said pulleys and having its inner end secured to afixed point, and means for vertically moving the inner end of said jib,said jib and radius rod being so proportioned and connected that thedownward 'vertical movement of the inner end of the jib is equal to thevertical rise of the outer end thereof, whereby the load will travel ina horizontal path during the lutling and the center of gravity of thejib will move parallel thereto.

5. In a crane, the combination with a ver tical support, of a cantaliverjib, a radius rod for suspending the jib to the upper part of thesupport, the said radius rod being of a length equal to a quarter of thelength of the jib and being attached to the latter at a point situated aquarter of the length of the jib fro-m the bottom end thereof and arunway upon or in connection with the lower part of the support in whichthe bottom end of the jib moves vertically, substantially ashereinbefore described.

ALFRED HILLYARD MITCHELL.

Witnesses:

JOI-1N E. BoUsFIELD C. G. RIDPEN.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents, Washington, D. C.

